Added support for scaling the output

* Added "Scale" user option, which can either by "Auto" or an explicit
  scaling factor. Its maximum value depends on the current resolution.

  The "Auto" factor is based on keeping the logical resolution on at
  least 800x600, wheres the maximum scale is based on keeping the
  logical resolution on at least 640x480.

* Enabled support for High DPI. This means the rendering target can now
  have a different resolution than the window size, which can happen on
  macOS, Windows and Wayland. The resulting scale is multiplied by the
  above user-controlled scale.

  Currently, this looks ugly for non-integer scales, which are not used
  on macOS and can only be configured on some Wayland compositors.

  Has not been tested on Windows.

* Simplified OpenGL initialization (moved out of _beginDraw).

* Made sure _beginDraw/_endDraw sets a clip area also for SDLGraphics.

1 files changed, 90 insertions, 16 deletions

diff --git a/src/gui/setup_video.cpp b/src/gui/setup_video.cpp
index 6f2f0d26..21f1935a 100644
--- a/src/gui/setup_video.cpp
+++ b/src/gui/setup_video.cpp
@@ -148,6 +148,40 @@ private:
     std::vector<DisplayMode> mDisplayModes;
 };
 
+/**
+ * The list model for choosing the scale.
+ *
+ * \ingroup Interface
+ */
+class ScaleListModel : public gcn::ListModel
+{
+public:
+    ScaleListModel(const VideoSettings &videoSettings)
+        : mVideoSettings(videoSettings)
+    {}
+
+    void setVideoSettings(const VideoSettings &videoSettings)
+    {
+        mVideoSettings = videoSettings;
+    }
+
+    int getNumberOfElements() override
+    {
+        return mVideoSettings.maxScale() + 1;
+    }
+
+    std::string getElementAt(int i) override
+    {
+        if (i == 0)
+            return strprintf(_("Auto (%dx)"), mVideoSettings.autoScale());
+
+        return strprintf(_("%dx"), i);
+    }
+
+private:
+    VideoSettings mVideoSettings;
+};
+
 
 static const char *overlayDetailToString(int detail)
 {
@@ -186,8 +220,10 @@ Setup_Video::Setup_Video():
     mSDLTransparencyDisabled(config.getBoolValue("disableTransparency")),
     mWindowModeListModel(new StringListModel({ _("Windowed"), _("Windowed Fullscreen"), _("Fullscreen") })),
     mResolutionListModel(new ResolutionListModel),
+    mScaleListModel(new ScaleListModel(mVideoSettings)),
     mWindowModeDropDown(new DropDown(mWindowModeListModel.get())),
     mResolutionDropDown(new DropDown(mResolutionListModel.get())),
+    mScaleDropDown(new DropDown(mScaleListModel.get())),
     mVSyncCheckBox(new CheckBox(_("VSync"), mVideoSettings.vsync)),
     mOpenGLCheckBox(new CheckBox(_("OpenGL (Legacy)"), mVideoSettings.openGL)),
     mCustomCursorCheckBox(new CheckBox(_("Custom cursor"), mCustomCursorEnabled)),
@@ -232,9 +268,11 @@ Setup_Video::Setup_Video():
     mResolutionDropDown->setSelected(mResolutionListModel->getIndexOf(mVideoSettings.width,
                                                                       mVideoSettings.height));
     mResolutionDropDown->setEnabled(mVideoSettings.windowMode != WindowMode::WindowedFullscreen);
+    mScaleDropDown->setSelected(mVideoSettings.userScale);
 
     // Set actions
     mWindowModeDropDown->setActionEventId("windowmode");
+    mResolutionDropDown->setActionEventId("resolution");
     mCustomCursorCheckBox->setActionEventId("customcursor");
     mParticleEffectsCheckBox->setActionEventId("particleeffects");
     mDisableSDLTransparencyCheckBox->setActionEventId("disableTransparency");
@@ -248,6 +286,7 @@ Setup_Video::Setup_Video():
 
     // Set listeners
     mWindowModeDropDown->addActionListener(this);
+    mResolutionDropDown->addActionListener(this);
     mCustomCursorCheckBox->addActionListener(this);
     mOpenGLCheckBox->addActionListener(this);
     mParticleEffectsCheckBox->addActionListener(this);
@@ -270,11 +309,13 @@ Setup_Video::Setup_Video():
     place.getCell().setHAlign(LayoutCell::FILL);
 
     place(0, 0, new Label(_("Window mode:")));
-    place(1, 0, mWindowModeDropDown, 2);
+    place(1, 0, mWindowModeDropDown, 2).setPadding(2);
     place(0, 1, new Label(_("Resolution:")));
-    place(1, 1, mResolutionDropDown, 2);
-    place(0, 2, mVSyncCheckBox, 4);
-    place(0, 3, mOpenGLCheckBox, 4);
+    place(1, 1, mResolutionDropDown, 2).setPadding(2);
+    place(0, 2, new Label(_("Scale:")));
+    place(1, 2, mScaleDropDown, 2).setPadding(2);
+    place(0, 3, mVSyncCheckBox, 4);
+    place(0, 4, mOpenGLCheckBox, 4);
 
     place = getPlacer(0, 1);
     place.getCell().setHAlign(LayoutCell::FILL);
@@ -304,24 +345,29 @@ void Setup_Video::apply()
 {
     // Video mode changes
     auto &video = Client::getVideo();
-    auto videoSettings = video.settings();
+    mVideoSettings = video.settings();
+
+    mVideoSettings.windowMode = static_cast<WindowMode>(mWindowModeDropDown->getSelected());
 
     if (mResolutionDropDown->getSelected() > 0)
     {
         const auto &mode = mResolutionListModel->getModeAt(mResolutionDropDown->getSelected());
-        videoSettings.width = mode.width;
-        videoSettings.height = mode.height;
+        mVideoSettings.width = mode.width;
+        mVideoSettings.height = mode.height;
     }
 
-    videoSettings.windowMode = static_cast<WindowMode>(mWindowModeDropDown->getSelected());
-    videoSettings.vsync = mVSyncCheckBox->isSelected();
+    mVideoSettings.userScale = std::max(0, mScaleDropDown->getSelected());
+    mVideoSettings.vsync = mVSyncCheckBox->isSelected();
 
-    if (video.apply(videoSettings))
+    if (video.apply(mVideoSettings))
     {
-        config.setValue("windowmode", static_cast<int>(videoSettings.windowMode));
-        config.setValue("vsync", videoSettings.vsync);
-        config.setValue("screenwidth", videoSettings.width);
-        config.setValue("screenheight", videoSettings.height);
+        config.setValue("windowmode", static_cast<int>(mVideoSettings.windowMode));
+        config.setValue("scale", mVideoSettings.userScale);
+        config.setValue("vsync", mVideoSettings.vsync);
+        config.setValue("screenwidth", mVideoSettings.width);
+        config.setValue("screenheight", mVideoSettings.height);
+
+        Client::instance()->checkGraphicsSize();
     }
     else
     {
@@ -387,9 +433,11 @@ void Setup_Video::apply()
 void Setup_Video::cancel()
 {
     // Set back to the current video mode.
+    mVideoSettings = Client::getVideo().settings();
+    mWindowModeDropDown->setSelected(static_cast<int>(mVideoSettings.windowMode));
     mResolutionDropDown->setSelected(mResolutionListModel->getIndexOf(mVideoSettings.width,
                                                                       mVideoSettings.height));
-
+    mScaleDropDown->setSelected(mVideoSettings.userScale);
     mVSyncCheckBox->setSelected(mVideoSettings.vsync);
     mOpenGLCheckBox->setSelected(mVideoSettings.openGL);
     mCustomCursorCheckBox->setSelected(mCustomCursorEnabled);
@@ -416,7 +464,7 @@ void Setup_Video::action(const gcn::ActionEvent &event)
 {
     const std::string &id = event.getId();
 
-    if (id == "windowmode")
+    if (id == "windowmode" || id == "resolution")
     {
         auto windowMode = static_cast<WindowMode>(mWindowModeDropDown->getSelected());
 
@@ -433,6 +481,12 @@ void Setup_Video::action(const gcn::ActionEvent &event)
         {
             mResolutionDropDown->setEnabled(true);
         }
+
+        refreshScaleList();
+    }
+    else if (id == "resolution")
+    {
+        refreshScaleList();
     }
     else if (id == "customcursor")
     {
@@ -488,3 +542,23 @@ void Setup_Video::action(const gcn::ActionEvent &event)
         }
     }
 }
+
+void Setup_Video::refreshScaleList()
+{
+    if (mResolutionDropDown->getSelected() > 0)
+    {
+        const auto &mode = mResolutionListModel->getModeAt(mResolutionDropDown->getSelected());
+        mVideoSettings.width = mode.width;
+        mVideoSettings.height = mode.height;
+    }
+    else
+    {
+        auto &videoSettings = Client::getVideo().settings();
+        mVideoSettings.width = videoSettings.width;
+        mVideoSettings.height = videoSettings.height;
+    }
+
+    mScaleListModel->setVideoSettings(mVideoSettings);
+    mScaleDropDown->setListModel(mScaleListModel.get());
+    mScaleDropDown->setSelected(mVideoSettings.userScale);
+}